1. Field of the Invention
This invention generally relates to a filter such as air filter. More particularly, the invention relates to a filter that can selectively remove a gaseous component such as aldehydes from a gas mixture, a method of making the filter and a method of removing a gaseous component from a gas mixture.
2. Description of the Related Art
A wide variety of materials have been suggested in the art as filters for tobacco smoke. Such filter materials include cotton, paper, cellulose, and certain synthetic fibers. These filter materials, however, only remove particulates and condensable components from tobacco smoke. They have little or no effect in removing certain gaseous components, e.g., aldehydes, from tobacco smoke.
In light of this, a number of additives have been proposed in the art to supplement the performance of the filter materials. Exemplary additives are mentioned in, for example, U.S. Pat. Nos. 2,815,761; 2,881,772; 2,968,306; 3,003,504; and 3,354,886. Some of the additives known in the art are effective in removing certain amounts of gaseous components from tobacco smoke. However, those additives also suffer from various drawbacks.
For example, U.S. Pat. No. 2,968,306 discloses the use of certain amino acids, such as glycine, for removing aldehydes in tobacco smoke. It has been discovered that while glycine can reduce the level of formaldehyde in tobacco smoke, it is not stable in the cigarette filter manufacturing process. Moreover, it releases ammonia odor during storage.
U.S. Pat. Nos. 4,604,110 and 4,534,775 disclose an air treatment filter element for removing odors from indoor air. The '110 and '775 patents disclose that the filter element is produced by contacting an adsorbent material such as zeolite, activated carbon and/or silica gel with a liquid for inhibiting growth of microorganism.
U.S. Pat. No. 4,892,719 discloses a race filter for removal of indoor pollutants such as formaldehyde or acidic gases such as SO2, SO3, NOx and H2S. The fitter includes a polymeric coating with functional groups such as polyallylamine or polyvinylamine for reacting with formaldehyde or acrolein.
U.S. Pat. Nos. 4,227,904; 4,374,814; 4,547,350; and 4,724,242 disclose filter arrangements for purifying air. The '904 patent discloses a gas phase permeable filter for home applications such as ductless range hoods, room air purifiers, electronic air cleaners, air conditioners, and heating/ventilating systems and for commercial/industrial applications where fuel exhaust and/or manufacturing operations generate odorants such as sulfur dioxide, formaldehyde, phenols, etc. The odor removing filter can be incorporated in a filter arrangement which also removes smoke, dust, or other particulates. The odor removing material can be flakes, particles, pellets or granules and the filter material can be activated carbon flakes or granules or other substance such as impregnated activated alumina, both of which are adhesively bonded to a porous substrate. A filter is assembled by providing a U-shaped frame around the edges of two such substrates with the bonded particles facing each other. The '350 patent discloses an air filter such as fiberglass or open cell polyurethane which includes a thin layer of polymeric amine such as polyethylenimine, the coating being effective to react with aldehydes and acidic gases. The '242 patent discloses an open-celled foamed gypsum and carbonaceous material for absorbing gases such as carbon monoxide, sulfur dioxide, ozone, ammonia, nitrogen oxides and formaldehyde, the filter material being used as absorbent particles in diapers and undergarments. The '814 patent discloses a filter for removing formaldehyde with a solid shaped composition prepared by coating a solid substrate or impregnating a porous or fibrous substrate with a composition including one or more polyhydric water-soluble polymers and water.
While various filter arrangements have been proposed for the removal of pollutants, it is an object of the present invention to provide an improved air filter that can selectively remove aldehydes from ambient air.
Thus, it is an object of the present invention to provide a filter arrangement and, more particularly, an air filter that can selectively remove a gaseous component such as aldehydes from a gas mixture.